The objective of this project is an analysis of error-prone repair in bacteriophage T4. Most chemical and all radiation mutagenesis in T4 occurs via error-prone repair, and depends on the functions of the genes uvsW, uvsX, uvsY and virtually all genes required for DNA replication. We have recently obtained and characterized conditional (temperature-sensitive and amber) alleles of the X and Y genes. The ts mutants are of particular interest because they differentially affect three different traits of the mutants, namely suppression of a gene 49 (Holliday resolvase) defect, ultraviolet radiation sensitivity, and ultraviolet mutagenesis. We plan genetic tests of the effects of these mutations upon recombination (which also depends upon the WXY system), tests to ask whether recombination and mutagenesis are correlated, tests to determine whicdh other genes of DNA metabolism are required for ultraviolet mutagenesis, tests of the sensitivity of mutants of the WXY system to photodynamic inactivation mediated by isopsoralen, tests to determine if the putative "uvsZ" gene is involved in error-prone repair, and screens for temperature-sensitive uvsW mutations. We plan to purify uvsX proteins from cells infected with ts uvsX mutants and to compare their biochemical properties with those of the wildtype protein, in order to determine which biochemical differences correspond to changes in survival versus mutagenesis after ultraviolet irradiation. Later, we plan to conduct the same kind of analysis of uvsY proteins.